1. Field of the Invention
The present invention relates to a method of manufacturing toner.
2. Discussion of the Background
As toner for electrostatic charge image development for use in the image formation process by electrophotography, powder which is formed of toner particles containing a binder resin and coloring agent therein is typically used.
Depending on the function required, a charge control agent for imparting charges to particles, a magnetic material for imparting transport property to toner, and a release agent are admixed to a binder resin and a coloring agent followed by melting and kneading. Subsequent to cooling down and fixation, the kneaded mixture is finely pulverized by a pulverizer and then the resultant is classified according to a desired particle size. Also, a fluidizer, etc. can be added. In the case of a toner for use in a two-component development method, the toner obtained as described above is mixed with a magnetic carrier.
As the typical pulverizer, there are two types of pulverizers, which are: a jet air pulverizer (especially, a collision type air pulverizer) using a jet stream; and a mechanical pulverizer in which powder material is introduced for pulverization into a circular space formed by the gap between a rotor rotating at a high speed and stators arranged around the rotor. The mechanical pulverizer has drawn attention in terms of the environmental issue of recent years because the mechanical pulverizer can pulverize material with less energy than the jet air pulverizer and reduce production of excessively pulverized fine toner, which leads to improvement on yield constant.
To obtain a stably functioning toner, it is inevitable to stabilize the particle size distribution of a toner. Furthermore, a high productivity and a high yield constant are demanded.
In a typical and simple system using such a mechanical pulverizer, coarse powder classified by a coarse powder classifier is directly returned to the mechanical pulverizer. In this system, coarse material is supplied for pulverization from a pulverized material supply to a fine pulverizer. The pulverized material is sent to the coarse powder classifier and coarse powder is separated by classification. The rest is collected by a cyclone to obtain a pulverized product. The emission from the cyclone is discharged by a blower after fine powder is separated by a bug filter. The coarse powder classified by the coarse powder classifier is returned to the pulverizer for circulation. However, when the amount of supply of the coarse powder varies, the load on the pulverizer also fluctuates. The particle size distribution of the toner obtained in such a situation varies and is not stable. In addition, due to the fact that the density of dust in the pulverizer is not uniform but locally high, a problem arises such that toner melts and fixates between a rotor and stators, which prevents stable performance of the pulverizer. Furthermore, due to the load on the pulverizer, heat is generated therein, which leads to deterioration of material, especially deterioration of preservability thereof.
To solve the problems mentioned above, Japanese patent No. (hereinafter referred to as JP) 2833089 describes a technology The technology is that, in a closed loop treatment in which pulverized material is finely pulverized by a pulverizer; coarse powder having a particle diameter greater than a specified value is separated from the resultant by a rotation type air classifier; the coarse powder is supplied to the pulverizer again for fine pulverization treatment, the coarse powder is constantly supplied to the pulverizer in an amount ratio of not greater than 5 times as much as the amount of toner material supplied thereto. However, in this technology, a weight detection device is provided to a device which collects separated coarse powder and returns the coarse powder to the pulverizer again so that complicate control and operation of the closed loop system is inevitable. That is, this technology has a drawback that the facility and operation cost for conducting this method increases, which boosts the manufacturing cost of toner.
In addition, JP 3773063 describes a method of manufacturing toner. In the method, such a device is not controlled by the weight, and the load applied during pulverization is fed back to the amount of feed so that pulverization can be performed under a constant load. In this method, the obtained toner has a stable particle size distribution but an operation of reducing the amount of feed is conducted, which is not preferred in light of productivity.